The present invention generally relates to bearings and, more particularly, to foil thrust bearings.
The ready availability of ambient atmosphere as a bearing fluid makes fluid bearings particularly attractive for high speed rotating machinery. Some applications might include, for example, a turboalternator-generator and turbocompressor.
Fluid bearings generally comprise two relatively rotatable members (i.e., a bearing and a runner). A predetermined spacing between the bearing and runner is filled with a fluid such as air. Foils (or thin sheets of a compliant material) disposed in the spacing are deflected by the hydrodynamic film forces between the adjacent bearing surfaces. The foils thus enhance the hydrodynamic characteristics of the fluid bearing and also provide improved operation under extreme load conditions when normal bearing failure might otherwise occur. Additionally, these foils provide the added advantage of accommodating eccentricity of the relatively movable members and further provide a cushioning and dampening effect.
To properly position the foils between the movable bearing members, it has been common to mount a plurality of individually spaced foils on a foil or thrust bearing disk and position the disk on one of the bearing members. Another common practice has been to provide separate compliant stiffener elements or undersprings beneath the foils to supply the required compliance. Examples of typical foil thrust bearings are shown in U.S. Pat. Nos. 5,547,286; 4,871,267; 4,682,900; 4,668,106; 4,624,583; 4,621,930; 4,597,677; 4,459,047; 4,331,365; 4,315,359; 4,300,806; 4,277,113; 4,277,111; and 4,247,155.
Notwithstanding the inclusion of the above design characteristics, the load capacity of a foil thrust bearing still depends on the compliance of the bearing with pressure exerted by a fluid film developed between the bearing and the runner. The pressure profile for a thrust bearing varies, and in order to accommodate the optimal pressure profile and attendant fluid film thickness associated with maximum load capacity, the thrust bearing should be designed to provide a fluid film that correlates to the pressure profile.
To correlate the fluid film with the varying pressure profile, the shape of the fluid film can be altered. Such alteration can be primarily achieved by varying the design of three componentsxe2x80x94namely, the thrust bearing disk, the foils supported by the thrust bearing disk, and the underspring element or thrust bearing stiffener that supports the thrust bearing disk. However, a design variation in one of the three components can have a performance impact on one or both of the other two componentsxe2x80x94either advantageously or disadvantageously. Accordingly, if two (and even three) of the components are altered in design, the ability to predict the performance impact (either positively or negatively) on the thrust bearing decreases more than linearly.
As can be seen, there is a need for an improved foil thrust bearing. In particular, there is a need for a foil thrust bearing that provides improved performance, including increased load capacity. A further need is for a thrust bearing that has increased fluid film pressure to increase the load capacity. Also needed is an improved thrust bearing that includes a fluid film shape that better correlates to the pressure profile. Another need is for a thrust bearing that has increased damping for increased vibration load capability.
In an improved foil thrust bearing, the present invention provides a pair of members arranged for relative rotation with respect to one another, one of the members being adapted to rotatably support the other; a thrust bearing disk operably disposed between the relatively rotatable members, with the thrust bearing disk having at least one surface ramp and at least one separately formed foil disposed on the thrust bearing disk.
Also, in another improved foil thrust bearing, the present invention provides a pair of members arranged for relative rotation with respect to one another, one of the members being adapted to rotatably support the other; a thrust bearing disk operatively disposed between the relatively rotatable members, with the thrust bearing disk having a plurality of radial slots, a plurality of surface ramps, and a plurality of separately formed foils disposed on the thrust bearing disk and between the ramps; and an underspring element operatively disposed between the thrust bearing disk and one of the rotatable members, with the underspring element having a plurality of alternating upper and lower ridges.